Portable folding bicycle



FIG. 1 is a perspective view of the portable folding bicycle;

FIG. 2 is a right side view;

FIG. 3 is a left side view;

FIG. 4 is a front view;

FIG. 5 is a rear view;

FIG. 6 is a top view; and,

FIG. 7 is a bottom view. 

The ornamental design for an portable folding bicycle, as shown and described. 